1. Field of the Invention
The present invention relates to an optical transmission path coupling method and an optical transmission path coupling apparatus as well as an optical axis self-alignment tool for an optical inter-connection to be used for coupling optical transmission paths constituted by light emitting and receiving devices and a plurality of optical fibers for connecting between these devices, and relates more particularly to an optical transmission path coupling method and an optical transmission path coupling apparatus as well as an optical axis self-alignment tool capable of easily coupling a plurality of optical fibers to individual light emitting and receiving devices by accurately matching optical axes.
2. Description of the Related Art
Literature 1: "Optical Parallel Transmission", SC-5-2, at The 1996 Electronics Society Meeting of The Institute of Electronics Information and Communication Engineers of Japan.
Literature 2: "Plane Light Emitting Laser Two-dimensional Array Non-adjusted Core Loaded Push-Pull Type Module", LQE96-144 (1997-02), Shingaku Gihou.
As a conventional method of coupling an optical transmission path, the one as shown in FIG. 4 of the above-described literature 1 is known. According to this light emitting and receiving device, each device within the case is sealed and the inside of the case is filled with an inactive gas such as a nitrogen gas. By this arrangement, functional deterioration due to deterioration of the devices and generation of dew inside the devices and generation of dew between lenses and fibers is prevented. Further, errors inside the case are cancelled by adjustment at the time of optically coupling the devices.
On the other hand, as a method of fixing positioning of optical axes of a Si substrate loaded with the light emitting and receiving devices, a method shown in the above-described literature 2 is known. According to FIG. 4 and FIG. 7 of the literature 2, a Si substrate is positioned by utilizing guide holes for guide pins (standardized guide pins for an MPO connector). To be more specific, in a state that alignment bumps of an alignment head are engaged with alignment V holes of a Si substrate, the Si substrate is adsorbed by the alignment head, the guide pins of the alignment head are inserted into the guide pin holes of the package and the Si substrate is accurately positioned to the package, which is then fixed by soldering.
However, according to the above-described prior-art methods of coupling the optical transmission path, there have been the following problems.
The prior-art optical elements are weak in temperature characteristics, and therefore, are used under normal environments (under not high temperature or low temperature but under normal temperature environments). However, in recent years, the temperature characteristics of the optical elements have been improved substantially and there are an increasing number of optical elements that can function normally even under bad conditions such as under high-temperature or low-temperature environments. There are also many examples where the optical elements are used with necessity under severe conditions. This has generated other problems. Particularly, under low temperature environments, dew is generated between lenses and optical fibers. Namely, an external air including moisture is brought into contact with the surface of the optical elements cooled under low temperature environments, and dew is generated on this surface so that the dew interferes the transmission path, with a result that a transmitted light is diffusely reflected by the dew and can not be transmitted normally. As a result, there has been a problem that the function of the information transmission is lowered.
To cope with this situation, an inactive gas such as a nitrogen gas has so far been filled inside the apparatus and the apparatus has been sealed with a high-temperature waxing or the like. This method, however, has not been able to air-tight seal the inside completely, and has not been able to solve the basic problem. When the apparatus is sealed with a wax or the like, the optical elements can not be positioned in high precision, and the optical fibers and the module need to be adjusted at the final stage, which has aggravated the work efficiency. Further, when the adjustment at the final stage can not be done accurately, production yield is lowered and products near the finished product stage has to be abandoned, thus incurring a cost increase. Further, the inactive gas filling work has also been one of the elements of cost increase.
For preventing the generation of dew, there is also a method of directly coupling the front ends of the optical fibers and fusing them. This method however involves troublesome work for coupling and fusion, which is not efficient.
Moreover, when the optical coupling of the optical elements and optical fibers is carried out by using a connector, there is generated a space between these optical elements and optical fibers. Therefore, unless the optically coupled parts are sealed air-tight and are shielded from the external air, the quality of communication is deteriorated due to a generation of dew and an adhesion of dusts to the apparatus, resulting in an inability of communication in the worst case.